LEGUMES 



329 



tion of crops (Section 654). On account of the deep-rooting 

 habit of many of the plants of this family, they improve the 

 physical condition of the soil, penetrating the lower layers 

 and leaving chan- 

 nels to carry off 

 surplus water and 

 admit air when 

 the roots decay. 

 They add some 

 ayailable plant 

 food to the upper 

 layers of the soil 

 by bringing it up 

 from below. They 

 materially in- 

 crease the fertility 

 and improve the 

 physical condition 

 of the soil by add- 

 ing a large supply 

 of organic matter. 

 Lastly, they are 

 very important in 

 the rotation, be- 

 cause they have 

 power, through 

 the medium of 

 bacteria which 

 live on their roots, 

 to take nitrogen 

 from the air and 

 leave it in the soil available for the use of other plants. 

 439. How the Legumes Gather Nitrogen. Bacteria and 

 other forms of minute life often live on our useful plants as 

 parasites and do considerable injury, as in the case of the 



Figure 113. — Young plant of red clover, showing tuber- 

 cles on the roots. 



